A family of hormones, comprising insulin, insulin-like growth factors (I and II), bombyxin, molluscan insulin-related peptide and relaxin, has been identified and designated as "insulin-related." Blundell and Humbel, 1980, Nature 287:781-787; Bullesbach and Schwabe, 1991, J. Biol. Chem. 266:10754-10761. The proteins comprising this family of hormones represents a group of polypeptides having homologous primary and secondary structure but divergent biological functions.
Relaxin has been purified from a variety of species including porcine, murine, equine, shark, tiger, rat, dogfish and human. In the human, relaxin is most abundantly found in the corpus lutea (CL) of pregnancy. Mature human relaxin is a hormonal peptide of approximately 6000 daltons which facilitates the birth process by remodelling the reproductive tract before parturition. More specifically, relaxin appears to modulate the restructuring of connective tissues in target organs to obtain the required changes in organ structure during pregnancy and parturition. See, Hisaw, 1926, Proc. Soc. Exp. Biol. Med. 23:661-663; Schwabe, et al., 1977, Biochem. Biophys. Res. Comm. 75:503-570; James, et al., 1977, Nature, 267:544-546. A concise review of relaxin was provided by Sherwood, D. in The Physiologvy of Reproduction, Chapter 16, "Relaxin", Knobil, E. and Neill, J., et al. (eds.), (Raven Press Ltd., New York), pp. 585-673 (1988).
While predominantly a hormone of pregnancy, relaxin has also been detected in the non-pregnant female as well as in the male. Bryant-Greenwood, 1982, Endocrine Reviews 3:62-90; Weiss, 1984, Ann. Rev. Physiol. 46:43-52.
Two human gene forms encoding for human relaxin have been identified, (H1) and (H2). Hudson, et al., 1983, Nature 301 628-631; Hudson, et al., 1984, EMBO J., 3:2333-2339; and U.S. Pat. Nos. 4,758,516 and 4,871,670. Only one of the gene forms (H2) has been found to be transcribed in CL. When synthetic human relaxin (H2) and certain human relaxin analogs were tested for biological activity, the tests revealed a relaxin core necessary for biological activity as well as certain amino acid substitutions for methionine that did not affect biological activity. Johnston, et al., in Peptides: Structure and Function, Proc. Ninth American Peptide Symposium, Deber, C. M., et al. (eds.) (Pierce Chem. Co. 1985). As set forth in U.S. Pat. No. 5,166,191, the binding activity of native relaxin has been calculated to have a K.sub.D of about 1.3 nM (measure in uterus) or 1.37 (measured in normal heart).
Methods of making relaxin are described in U.S. Pat. No. 4,835,251 and in co-pending U.S. Ser. Nos. 07/908,766 (PCT US90/02085) and 08/080,354 (PCT US94/0699). Methods of using relaxin in cardiovascular therapy and in the treatment of neurodegenerative diseases are described in U.S. Pat. No. 5,166,191 and in U.S. Ser. No. 07/902,637 (PCT US92/06927) . Certain formulations of human relaxin are described in allowed U.S. Ser. No. 08/050,745.
In view of the diverse applications for relaxin currently being explored, identification of relaxin analogs retaining or having higher biological activity has been the focus of investigation. Until the present invention, however, a substantially biologically active analog of relaxin had not been identified.